The present invention relates to a control apparatus of a synchronous reluctance motor, and more particularly to a control apparatus for driving the motor with estimation of the angle of the rotor without using position sensor.
A conventional control apparatus of a synchronous reluctance motor is designed to obtain the angle information of a rotor by using a position sensor such as Hall element, resolver or optical encoder. Accordingly, the cost is increased by the portion of the position sensor, and the size of the synchronous reluctance motor is also increased.
As a control apparatus of the synchronous reluctance motor for realizing low cost and small size by omitting position sensors, generally, a control apparatus of the synchronous reluctance motor as shown in FIG. 23 has been known.
In FIG. 23, a main circuit includes an alternating-current power source 1, an AC/DC converter 2 for converting an alternating-current power into a direct-current power, a DC/AC converter 3 for converting a direct-current power into an alternating-current power, and a synchronous reluctance motor 5 driving with the alternating-current power converted by the DC/AC converter 3.
On the other hand, a control circuit includes current detectors 11a and 11b and a motor current detector 12 for detecting the motor current, a position and speed estimation unit 13 for estimating the position and speed of the synchronous reluctance motor, a speed control unit 14 for determining a current command so as to eliminate the speed error between the speed command given from outside and the estimated speed obtained from the position and speed estimation unit 13, a conduction phase distribution unit 15 for distributing the current command obtained from the speed control unit 14 into a torque current component and a field current component, a current control unit 17 for determining the voltage command so as to eliminate the current error of the torque current command and field current command, and the detected motor current, and a conduction distribution unit 18 for distributing the conduction signal into driving elements in the synchronous reluctance motor 5.
FIG. 24 is a sectional view showing a structure of a general synchronous reluctance motor 5. The synchronous reluctance motor 5 is composed of a rotor 8 and a stator 6.
In the control apparatus shown in FIG. 23, the position and speed estimation unit 13 determines the magnetic flux by using the information of the motor current command and voltage command. Next, an xcex1-xcex2 magnetic flux angle showing the angle based on the stationary coordinates of this magnetic flux is determined. Further, a d-q axis coordinate phase indicating the phase of this magnetic flux corresponding to the rotational coordinates is set. The d-q axis coordinate phase is subtracted from the xcex1-xcex2 axis coordinate angle to obtain an estimated angle. On the basis of this estimated angle, the synchronous reluctance motor 5 is controlled.
Further, the angle is estimated in two methods of low speed angle estimation and high speed angle estimation, and in the boundary of low speed region and high speed region, the angles estimated by two methods are synthesized by gradually changing the rate of the estimated angles to generate an estimated angle. In the low speed region, a current pulse is applied and the angle is obtained from the voltage response.
For example, the synchronous reluctance motor of driving system without using position sensor disclosed in Japanese Laid-open Patent No. 2001-197774 has low pass filter means for applying a low pass function to the voltage command, and weakens the low pass function when the rotor speed increases to eliminate effects of voltage pulse in the boundary region of low and high speed regions and change over the angle estimating methods stably, realizing the control of synchronous reluctance motor free from time delay in high speed region.
In the conventional configuration, however, the control calculation is complicated, and if the voltage control rate of the inverter is over 100% to be in so-called voltage saturation, or if the load fluctuates extremely, it is difficult to estimate the position or speed, and the motor drive control is unstable.
The invention is intended to solve these problems of the prior art, and it is hence an object of the invention to present a control apparatus of the synchronous reluctance motor building up a robust control structure withstanding voltage saturation and steep load fluctuations.
The motor control apparatus according to the invention is an apparatus for controlling a synchronous reluctance motor by using a reluctance torque caused by at least a change in inductance of the stator winding and a motor current.
In the control apparatus, a current detector detects the motor current flowing in the stator winding of the synchronous motor.
A position and speed estimation unit estimates an induced voltage of the synchronous reluctance motor from the detected value by the current detector and a voltage command which is a command to a voltage to be applied to the stator winding of the synchronous reluctance motor, and estimated rotor position and rotating speed of the synchronous reluctance motor on the basis of the estimated induced voltage.
A speed control unit determines a current command which is a command to a current to be supplied to the stator winding of the synchronous reluctance motor so as to eliminate the error of the estimated rotating speed by the position and speed estimation unit and a target value of the rotating speed given from outside.
A distribution unit distributes the current command from the speed control unit into a torque current command which is a torque current component of the current command and a field current command which is a field current component of the current command, on the basis of a predetermined current phase angle of the synchronous reluctance motor.
A torque current correction unit corrects the torque current command on the basis of the torque current command from the distribution unit and the estimated rotating speed from the position and speed estimation unit, so that a load torque generated by a load element of the synchronous reluctance motor coincides with the output torque of the synchronous reluctance motor.
A current control unit generates a voltage command so as to eliminate the error between the corrected torque current command from the torque current correction unit and the detected motor current from the current detector, and the error between the field current command from the distribution unit and the detected motor current obtained from the current detector.
A conduction distribution unit distributes conduction signals into driving elements in the synchronous reluctance motor on the basis of the voltage command.
The control apparatus of the invention, having such configuration, controls so that the load torque generated by the load element of the synchronous reluctance motor may always coincide with the output torque of the synchronous reluctance motor. As a result, a robust control structure is built up withstanding steep load fluctuations, and torque fluctuations are suppressed, and lower vibration and lower noise are realized.